This application is based on Application No.2000-301922, filed in Japan on Oct. 2, 2000, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a protective device for a vehicle starter used during cranking, and in particular, to a starter protective device which is capable of accurately determining an overrunning state of a starter motor even in the presence of noise and/or variations in the cycle of fluctuations in a battery voltage during an engine is being cranked, thereby to prevent damage to the starter motor due to unnecessary overrunning thereof after the engine has been started.
2. Description of the Related Art
In general, when a motor vehicle engine is started, the driver hears the sound generated by the engine at the same time when he or she turns on a starter switch, and upon sensing a characteristic sound generated at the commencement of engine starting, the driver turns off the starter switch.
Since the engine generation sound is becoming more and more quiet along with the improved performance of engines in recent years, however, there are many cases in which it is quite difficult for the driver to accurately sense or discriminate the engine generation sound from other sounds or noise originated from a variety of sound sources.
Moreover, for large-scale vehicles such as trucks in which the distance from the driver""s seat to the engine is long, it is extremely difficult for the driver seating in his or her seat in a passenger compartment to catch the sound generated by the engine installed in an engine room remote from the driver""s seat, as a consequence of which it becomes difficult for the driver to promptly turn off the starter switch as soon as the engine has been started, so as to avoid the overrunning state of the starter motor.
In order to prevent the motor damage or the like due to such an overrunning of the starter motor (i.e., the state in which the starter continues operating though the engine has begun to operate autonomously), there have been proposed a variety of starter protective devices.
In case of a conventional starter protective device disclosed in Japanese Patent Application Laid-Open No. 10-184503 for example, timing of the commencement of starting of an engine is automatically detected from the cycle of fluctuations in the battery voltage waveform during cranking, whereby the starter motor is turned off at that timing.
That is, during engine starting, after the battery voltage first decreases rapidly, the load on the starter motor is periodically increased at angle positions corresponding to the compression strokes of engine cylinders, so there is obtained a waveform of cyclic fluctuations in the battery voltage during cranking.
Thereafter, when the engine commences starting, the load on the starter motor decreases suddenly and an alternator comes to perform power generation, so that the cycle of the waveform of fluctuations in the battery voltage becomes long, and at the same time the battery voltage is rising.
Thus, the cycle of the waveform of fluctuations in the battery voltage is measured, and when it reaches a predetermined value or above, a determination is made as to whether the starter motor commences to be overrun, and if so, the starter motor can be turned off.
That is, based on the fluctuations in the battery voltage generated by the power supply from the battery to the starter at the time of engine starting, it is detected whether the engine has entered an autonomously operating state, and it is possible to compulsorily interrupt the operation of the starter at the instant when the engine has begun autonomous operation.
As a result, it is possible to prevent the internal component parts (e.g., starter motor, etc.) of the starter from being damaged, which would otherwise result from starter""s excessive overrunning.
However, the waveform of fluctuations in the battery voltage during cranking varies greatly, for example, the cycle of fluctuations is increased owing to a cold engine state upon starting of the engine, and in addition to this, the results of determinations on the cycle of fluctuations also become different under the influence of noise superposition. Therefore, the reliability in the determination of overrunning according to the above-mentioned conventional device is low and hence it is difficult for the conventional device to provide a satisfactory starter protective function.
As can be seen from the foregoing, the conventional starter protective device has a problem that the commencement of overrunning can not be determined accurately thanks to the influences of the engine condition, noise and so on at the time of engine starting, thus making it impossible to achieve a satisfactory protective function for starters.
The present invention is intended to obviate the problems as referred to above, and has for its object to provide a starter protective device which is capable of accurately determining the commencement of overrunning (i.e., timing of the commencement of starting of an engine) even in the presence of variations in the cycle of fluctuations in the battery voltage, noise and so on, thereby to prevent a starter from being overrun after starting of an engine in a reliable manner.
Bearing the above object in mind, the present invention resides in a starter protective device comprising an electronic control unit supplied with a battery voltage from a battery mounted on a vehicle, a starter switch connected with an output terminal of the battery, a main contactor adapted to be driven under the control of the electronic control unit in response to the starter switch being turned on, and a starter motor adapted to be driven to operate by the battery voltage supplied thereto from the battery through the main contactor when the main contactor is turned on or closed. The electronic control unit includes an overrunning determination section for determining when the starter motor commences overrunning, and a starter motor cut-off section for interrupting or opening the main contactor when it is determined that the starter motor commences overrunning. The overrunning determination section detects a change over time of the battery voltage after the starter switch has been turned on, and determines that the starter motor commences overrunning when the battery voltage remains unchanged without any increase or decrease over a predetermined time.
In a preferred form of the present invention, the overrunning determination section includes a storage section for storing a waveform value of fluctuations in the battery voltage in time steps, a comparison unit for sequentially comparing a current voltage value of the battery voltage and a plurality of past voltage values thereof stored in the storage section according to the time steps, and a determination signal generating section for generating an overrunning determination signal indicative of the commencement of overrunning of the starter motor when comparison results of the comparison unit exhibit the same results over the predetermined time.
In another preferred form of the present invention, the storage section stores the waveform values of fluctuations in the battery voltage in a plurality of mutually different time steps. The comparison unit includes a plurality of comparison sections for individually comparing the current voltage value and the plurality of past voltage values stored in the storage section. The overrunning determination section includes a logical arithmetic operation section for logically summing the respective comparison results of the comparison sections. The determination signal generating section generates the overrunning determination signal when an output level of the logical arithmetic operation section remains the same over the predetermined time.
In a further preferred form of the present invention, the storage section stores, as the plurality of past voltage values, at least two voltage values at previous time points 10 ms and 20 ms, respectively, before the current time.
In a yet further preferred form of the present invention, the predetermined time is initially set to 500 ms.
In a still further preferred form of the present invention, the overrunning determination section includes a predetermined time calculation section for calculating the predetermined time, and the predetermined time calculation section variably sets the predetermined time based on a past record value of a transition cycle of the comparison results of the comparison unit.
In a further preferred form of the present invention, the predetermined time is set to 1.5 to 2 times the past record value of the transition cycle of the comparison results.
The above and other objects, features and advantages of the present invention will become more readily apparent to those skilled in the art from the following detailed description of preferred embodiments of the present invention taken in conjunction with the accompanying drawings.